Electron discharge apparatus



Patented Dec. 1, 1931 UNITED STATES PATENT OFFICE BENJAMIN r. MIESSNER,or soon: ORANGE, NEW, JERSEY, ASSIGNOR, BY MizsnE As- SIGNMENTS, TORADIO CORPORATION or PORATION OF DELAWARE V i I ELECTRON DISCHARGEAPPARATUS Application filed June 8, 1927; Serial No. 197,314.

uum tubes adapted for use in a system Wherein the filament of the tubeis heated by alternating or other I unsteady current flowingtherethrough.;- A a V Heretofore the use of unsteady current in the;filament has produced a number of effects which have contributed toagreater or less extenttoward' producing disturbing current variationsin the'plate circuit ofthe tube. Thus during momentary recurring periodsof low current the temperature of the filament falls and'the electronemission from the heated filament is momentarily reduced, which tends todecrease the flow of electrons to theplate electrode. Also thevariations in the diflerence of potential between different portions ofthe filament tends to cause variations in the plate current, Portions ofthe filament which are momentarily at higher positive potential have theeffect of diverting from the plate some of the electrons emitted fromthe lower potential portions of the filament, thus periodically robbingthe plate of some of its supply of electrons.

The reduction or elimination of disturbing hum efiects may lee-effectedby the use of a filament of special design as is disclosed in mycopending application, Serial No. 191,- 195, filed May 13,1927. issuedJune 18, 1929 under Patent No. 1.718,059. In the'present application Idisclose a means additional to the filament for reducing or controllingthe bum variations particularlvithose variations which are; caused bythe robbing effect above referred to.

In the particular form of my-invention herein disclosed, my improvedvacuum tube has a plate, filament and grid; The grid comprises a flatcoil. of wire surrounding the'filament, which'filament is ofthe V-typeand extendirv between the legs of, the V is a metal shield inltheaformof a strip or plate-which is secured at points along. its edgesto the turns of the grid coil. In this form of my invention'the shield,because of its connection to the grid, is electrically part of the grid,

and when the grid is biased negatively'the shield creates anelectrostatic field of-nega+ two potential in the space between the legsAMERICA, on NEW Yo uz, a. Y., A 003- of the filament. This fieldprevents electrons emittedfrom the negative leg of thefilament frompassing over to the positive leg and, so reducespor eliminatestherobbing effect. f

Also-the shield, Which extends between the legs of the filament, actsas'a mechanical bar;

rier to the flow of electrons between the legs.

also the-shield willserve tovminimiz e the robbing efi'ect.

While I illustrate my invention as applied to a vacuum tube having afilament ofthe-V- type, I do not wish to limit the invention -to usewith a filament of any particular sform. Theinvention in its broaderaspects involves merely interposing a barrier to the flow of electronsfrom one portion of the filament through the evacuated space to anotherportion, or creating a field of force in the path which the electronswould normally follow in passing from one portion to another of thefilament, which field has the effect of reducing the How of electronsalong such path.

Features and advantages of my invention other than those above notedwill be apparent from the following description taken in connection withhe accompanying drawings, which shows a vacuum tube and connectedcircuits, the tube being shown in perspective and a portion of the plateelectrode of the tube being broken away to disclose'the filament andgrid structure.

Figure 1 illustrates my invention as applied to a V-type filament.Figure 2 illustrates the invention as applied to an M-type filament. IThe tube 9 as shown encloses. an evacuated space in which are located afilament-10, grid 1-1 and plate electrode 12. The filament 10 is of theV-type' formed of lengths orlegs 14 connected at their lower ends bynickeltubes 15 to leading-in wires 16, which wires are sealed throughthe glass neck of-the-tube. v

ing wound around spaced vertical rods 24.

The lower ends of the rods 24 are sealed in the glass neck of the tubeand one of the rods 24 connects with a wire 26 which forms the'lea'ding-in'terminal of the grid.

The plate 12, which is spaced from and sur rounds the grid 11, is formedof two thin sheet metal side members 28 bent toward one another andjoined together near their side edges. The outer edges ofthe members 28are pinched around supporting rods 29, which rods are sealed at theirlower ends in the glass neck of the tube. A wire 30 connected with oneof the rods 29 forms the leading-in terminal of the plate. spring rod20, which supports the filament from the top, is in turn supported fromthe top of one of the rods 29 by'aninsulating glass member 32.

Positioned between the two legs 14 of the filament and extending atapproximately right" angles to the plane of the filament is a thin metalstrip or shield 35, which is welded at points along its side edges tothewire v turns ofthe grid coil. This strip may be perforated or otherwiselightened in weight. The circuit diagram of the drawings shows thefilament heating circuit supplied from the secondary S of an alternatingcurrent transformer the: plate circuit energized from a source B ofdirect current, and a source of potential C 'for'supplying a negativebiasing voltage to the grid 11. The plate and grid circuits areconnected tothe filament supply circuit through an adjustable tap T anda-potentiometer resistance P connected across the secondary S. The tubeconnected in the manner shown may be used as a radio fretector.

Due to the alternating heating current in the filament one leg of thefilament is alter nately of positive and negative potential with respectto theother leg. The strip 35 forms a shield between thelegs ofthefilament and in the form of invention shown, this strip be ing connectedto the grid coil. ismaintained 'quency or audio frequency amplifier, orde- 'bythe sourceC at a potential which-is negative with respect to thenegative leg of the plate. This shield operates in the manner abovedescribed to prevent electrons emitted from the" negative leg frompassing to' the positive leg and-.in this manner reduces the robbingeffect. I p When the filament is in the form of a W instead of a V threeshields may be employed, one between each pair oflengths.

Figure 2' shows a filament in the form ofan MP The arm 20has two hooks18 to support the upper bends, and the hook 118, which is embedded inthe press, supports the/center lower bend of the M. Positioned betweeneach pair of legs of the filament 100 and supported by the grid coil 11is a strip 35, as in Figure 1. In Figure 2 the anode and other elementshave been omitted for the sake of clearness. It is apparent that insteadof the 7 M-type of filament a. W-type may be used.

In certain cases the shield 35 may be formed of non-conducting materialsuch as glass, the

. glass shield functioning as a barrier between the diflt'erent portionsof the filament and so 7 reducing the flow of electrons between theportions. A tube with a non-conducting shield may be used when it isdesired to operate atube without-negative grid bias, as is often thecase with detector tubes. 8

' In my patent hereinbefore referred to, I

disclosed avacuum tube designed for operation with alternating currentin the filament andwherein provision is made'for reduction ofdisturbing-hum variations in the plate circuit by the use of a filamentof large diameter operated at lowtempt-rature and low voltage, or by theuse inv a single tube of two of such filaments connected in parallel. Inthe present invention, if desired, the filament "10 maybe formed ofrelatively thin wire designed for operation atrelatively high voltage. Imay, however,'secure the advantages gained of low voltage and lowtemperature filament of large diameter and relatively low resistance. rThe diameter ofthe filament 10 may be made sufficiently large that itsresistance is practically the same as the two parallel connectedfilaments'disclosed in my oopending application. When so made thefilament 10 may beoperated at approximately the samelow voltage which Iemploy for operation of the two filaments in'parallel.

The temperature of operation of the filament 195 10 at such low voltagewill be low and this, together with the high heat storage capacity ofthe large filament, will minimize the temperature variations of thefilament and so reduce the disturbing hum variations in the no platecircuit. I

V For the sake of brevity and definiteness in setting forth theinvention to be defined in the claims annexed hereto, I shall use thedistinctive terms and definitions thereof as applied to my improved tubeand set forth in my patenthereinbefore referred to, specifically inlines 113, page 5 to line 25, page 6 thereof.

In-tubes using two spaced filaments conpower. In the form of filamentdisclosed in no operation by employing, as the filament 10, a

the present application this heat loss is greatly reduced because onlytwo lead wires are necessary instead of four. The supporting hook 18which engages a bend at'the top of the filament is ofvery thin wire andconducts a relatively small amount of the heat away from the filament.

I claim 1. In an electron discharge tube, a plate, a V-shaped filament,a grid comprising a coil of Wire surrounding said filament, and a flatstrip secured at points along its side to the turns of said coil, saidstrip extending laterally between the two legs of said filament.

2. In an electron discharge tube, a plate, a current-carrying V-shapedelectron emissive filament, a grid surrounding said filament, and a fiatmetallic screen between the legs of said filament having its plane atright angles to the plane of said V-shaped filament and conductivelyconnected to "said grid.

In testimony whereof I hereunto afiix my signature. I

BENJAMIN .F. MIESSNER-

